Intra-aortic balloon catheter having a dual sensor pressure sensing system

ABSTRACT

A balloon catheter has a balloon membrane, a tip connected to the distal end of the balloon membrane and an outer tube connected to the proximal end of the balloon membrane for supplying a medium for inflating and deflating the balloon membrane. A pressure sensor, such as a fiber optic sensor, may be mounted in a pocket in the tip. The pocket may be filled with a flexible substance which both communicates pressure to and protects the pressure sensor. A membrane may overlie the pocket to prevent leakage of the flexible substance therefrom.

The present application is a continuation of U.S. application Ser. No.10/308,638, filed Dec. 3, 2002, now U.S. Pat. No. 6,935,999, which is acontinuation of U.S. application Ser. No. 09/735,076, filed Dec. 12,2000, now U.S. Pat. No. 6,616,597.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a catheter having enhanced pressure sensingcapabilities. More particularly, the invention relates to a ballooncatheter having a micromanometer connected to the catheter and also afluid-filled transducer system for adjusting micromanometer pressuremeasurements.

2. Description of the Prior Art

A key function of many catheters is that of continuously monitoringblood pressure. In many cases, this monitoring must be performed withaccurate measurement of high frequency components. For example, reliabledetection of the dicrotic notch of the aortic blood pressure waveformtypically requires a pressure signal having a bandwidth of 15 Hz orbetter. Detection of the dicrotic notch is generally used for theinflation/deflation timing of an intra-aortic balloon (“IAB”) catheter.

Conventional invasive pressure monitoring is performed with low-costfluid-filled transducers. A typical disposable monitoring kit, inclusiveof all tubing, a continuous flush device, and a pre-calibratedtransducer is very affordable. Unfortunately, these systems have severaldrawbacks. One major drawback is that bubbles or clots in the monitoringlines can reduce the frequency response of the system to a level below15 Hz, creating an “overdamped” condition. In other cases, thecharacteristics of the catheter and tubing can result in “ringing”,which is associated with an underdamped condition. Furthermore,fluid-filled catheters can suffer from “catheter whip” (motionartifact), which is manifested as one or more high frequency deflectionsin the pressure signal. These problems can degrade the usefulness of thesignal in applications such as intra-aortic balloon pumping (IABP). Inparticular, it is difficult, if not impossible, to automatically provideoptimal timing of IABP using a pressure signal with a frequency responsebelow 15 Hz, or using signals with ringing or whip artifacts that mimicthe physiologic dicrotic notch.

Another means for monitoring blood pressure is to use a micromanometer,such as marketed by companies such as Millar, Endosonics, and Radi. SeeU.S. Pat. Nos. 5,431,628 and 5,902,248, herein incorporated byreference. These devices can have excellent frequency responses, withsystem bandwidths greater that 200 Hz. They are not subject to thenegative effects of bubbles and catheter whip, and retain goodperformance even in the presence of small blood clots. Unfortunately,they are very expensive, prone to signal drift, and can suffer fromelectrical interference. A common source of electrical interference inthe setting of IABP therapy is the use of electrosurgery. In thissituation, it is desirable to maintain a reliable pressure signal withwhich to trigger the balloon, as the ECG signal which normally triggersIABP operation becomes completely unreliable. Conventional fluid-filledtransducer systems are relatively immune from this type of interference.

If the above problems were solved, micromanometers could potentially beused in conjunction with IABP systems and other catheters to measureblood pressure. Attempts have been made to use micromanometers for IABPtiming, see U.S. Pat. Nos. 3,585,983 and 4,733,652, herein incorporatedby reference. These attempts proved to be unreliable, as the device maybe damaged during insertion and is also prone to signal drift. Toaddress the drift issue, U.S. Pat. No. 5,158,529, herein incorporated byreference, discloses a method for rezeroing the micromanometer by usingthe pressure from a partially filled balloon as it rests in the aorta.However, this method requires momentary interruption of IABP, which maybe harmful to the critically ill patient.

While standard IAB catheters incorporating a fluid-filled transducerpressure measurement system or IAB catheters incorporatingmicromanometers may be suitable for the particular purpose employed, orfor general use, they would not be as suitable for the purposes of thepresent invention as disclosed hereafter.

SUMMARY OF THE INVENTION

Accordingly, there is a need for a reliable and affordable pressuremonitoring approach that has high bandwidth pressure sensing, low signaldrift, and freedom from electrosurgical interference. There is also aneed to incorporate this technology into intra-aortic balloon cathetershaving small cross sectional profiles.

The invention is an IAB catheter system having enhanced blood pressuresensing capability. The IAB catheter has a micromanometer, or any highfidelity sensor, built into the tip of the IAB or connected to anotherpart of the catheter, and a fluid-filled transducer kit connected to they-fitting of the IAB. The IABP console, including a processor,continuously monitors and compares signals from both the micromanometerand the fluid-filled transducer. The signal from the micromanometer maybe continuously displayed, and either continuously or intermittentlyadjusted for baseline drift by comparing it to that of the fluid-filledtransducer. The adjustment is preferably made by comparing mean bloodpressures as indicated by the two sources.

The IABP console could also monitor the micromanometer's signal for thepresence of electrosurgical interference, mechanical damage, or anyother possible causes of signal error. If significant errors aredetected, the system automatically reverts to the use of the signal fromthe fluid-filled transducer system. The system also allows the user tomanually select the use of the fluid-filled transducer, in the eventthat electrosurgical interference was anticipated.

To the accomplishment of the above and related objects the invention maybe embodied in the form illustrated in the accompanying drawings.Attention is called to the fact, however, that the drawings areillustrative only. Variations are contemplated as being part of theinvention, limited only by the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are depicted by like reference numerals.The drawings are briefly described as follows.

FIG. 1 is a perspective view of the system of the present invention.

FIG. 2 is a detailed longitudinal cross sectional view of flush device34 in FIG. 1.

FIG. 3 is longitudinal cross sectional view of a distal portion of IABcatheter 10 in FIG. 1.

FIG. 3A is a perspective view of distal end of inner tube 58, shownindependent of catheter 10, with pressure sensing line 24 connected toan outer surface of inner tube 58.

FIG. 3B is a perspective view of a distal end of inner tube 58, shownindependent of catheter 10, with pressure sensing line sandwichedbetween an outer surface of inner tube 58 and an outer layer.

FIG. 3C is a perspective view of a distal end of inner tube 58, shownindependent of catheter 10, with pressure sensing line 24 embedded inthe wall of inner tube 58.

FIG. 4 is a longitudinal cross sectional view of a distal portion of aco-lumen IAB catheter having a pressure sensor embedded in the tip.

FIG. 4A is a transverse cross section of the co-lumen IAB, taken alonglines 4A—4A in FIG. 4.

FIG. 5A is a perspective view of a distal end of the inner tube 58 andthe catheter pressure sensor 22, illustrating a first connection scheme.

FIG. 5B is a perspective view of a distal end of the inner tube 58 andthe catheter pressure sensor 22, illustrating a second connectionscheme.

FIG. 5C is a perspective view of a distal end of the inner tube 58 andthe catheter pressure sensor 22, illustrating a third connection scheme.

FIG. 6 is a longitudinal cross section of tip 20 and a distal end ofinner tube 58 and balloon membrane 30.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the system of the present invention comprising anintra-aortic balloon (“IAB”) catheter 10, an intra-aortic balloon pump(“IABP”) 12, a monitor 14, a drip bag 16, and a drip bag holder 18. FIG.1 is a perspective view of the system with the IAB catheter 10 in theforeground and the IABP 12 is the background for clarity. The IABcatheter 10 contains a catheter pressure sensor 22 connected to its tip20 and a Y-fitting 36 on its proximal end. The catheter pressure sensor22 is connected to the IAB pump 12 via pressure sensing line 24, shownas ghost lines in the IAB catheter 10. Inflate/deflate tube 26,connecting an outer lumen of the IAB catheter 28 (see FIGS. 3–4) and theIABP 12, is used for inflation and deflation of a balloon membrane 30connected between the tip 20 and a distal end of the IAB catheter 10.Drip tube 32 connects the pressurized drip bag 16 to a flush device 34.Saline tube 38 connects the flush device 34 with an inner lumen 60 ofthe IAB catheter (see FIGS. 3–4). Clamp 40 connects the flush device 34to the drip bag holder 18.

The details of flush device 34 can be seen in FIG. 2. The flush device34 comprises a flush device wall 52, a microbore passage 42, a fastflush seal 44 having a handle 46, flush device lumen 48, and a fastflush variable lumen 50. Pressure sensor 40 is located in flush device34 and communicates with IABP 12 via an independent line (not shown),which may exit through a hole (not shown) in flush device wall 52, or inany other means known in the art for electrical devices to communicate.Saline, or another appropriate working fluid or gas, flows through theflush device lumen 48 through the microbore passage 42 at a very slowrate, approximately 3 cc/hour. The pressure on the side of the flushdevice 34 connected to drip bag 16 equals the pressure in the drip bag16, generally 300 mmHg. The pressure on the opposite side of the flushdevice 34 adjacent the pressure sensor 40 equals the blood pressure ofthe patient being treated with the IAB catheter 10. The fast flush seal44 is shown in an open state, however, during therapy fast flush seal 44is forced against seat 54 by the flush device wall 52, and therefore,does not allow saline through fast flush variable lumen 50. In order tofast flush saline tube 38 and bypass microbore passage 42, handle 46 canbe pulled away from the flush device 34 such that fast flush seal 44 islifted off seat 54. During normal operation, however, saline drip isforced through microbore passage 42. Note that the flush device 34 maybe replaced with any other known flush device in the art having similarfunction.

The IABP 12 has incorporated therein a processor that controls theinflation/deflation timing of the balloon membrane 30. Alternatively,the IABP 12 can be connected to a computer or any other type of controlmechanism known in the art. The IAB catheter 10 is typically insertedinto the femoral artery and moved up the descending thoracic aorta untilthe distal tip 20 is positioned just below or distal to the leftsubclavian artery. The proximal end of the catheter remains outside ofthe patient's body. The patient's central aortic pressure is used totime the inflation and deflation of balloon membrane 30 and thepatient's ECG may be used to trigger balloon membrane 30 inflation insynchronous counterpulsation to the patient's heartbeat.

In the preferred embodiment, IABP 12 continuously monitors and comparessignals from both saline pressure sensor 40 and catheter pressure sensor22. The signal derived from catheter pressure sensor 22 may becontinuously displayed on monitor 14 and either, continuously orintermittently adjusted for baseline drift or other errors by comparingit to that of saline pressure sensor 40. The adjusted signal isdisplayed on monitor 14 and is used to time the inflation and deflationof the balloon membrane.

The balloon membrane is inflated coincident with closure of the aorticvalve and is contracted or deflated prior to cardiac ejection.

It is preferred that the adjustment be made by comparing mean bloodpressures as indicated by the two sources. In operation pressure wouldbe measured over a predetermined period of time via both the catheterpressure sensor 22 and the saline pressure sensor 40. An indicated meanpressure, based on the catheter pressure sensor 22 measurements, and atrue mean pressure, based on the saline pressure sensor 40 measurements,are calculated. If the indicated mean pressure differs from the truemean pressure by less than a predetermined amount, the catheter pressuresensor 22 measurements are displayed without correction; otherwise thecatheter pressure sensor measurements are corrected prior to displaysuch that the indicated and true mean pressures are equal.Alternatively, the pressures can be compared on a continuouspoint-by-point basis and an adjustment made if and when a predeterminedpressure differential is reached.

IABP 12 may be programmed to provide options as to which sensor isrelied on in any given situation and as how to compare the signals fromboth sensors and use the information contained in these signals to mostaccurately measure blood pressure. Note also, that in an alternativeembodiment of the invention, a pressure cuff or other external orinternal independent device known in the art may replace or act as abackup to the saline pressure sensor 40. The reading from theindependent external or internal blood pressure measurement device maybe used to correct the drift in the catheter pressure sensor 22 readingin the same manner as used with the saline pressure sensor 40 reading.Use of such an independent external or internal measurement device maybe necessary to adjust for drift in tip sensors in intra-aorticcatheters without an inner tube and associated saline pressure sensor.

The adjustment to the catheter pressure sensor 22 readings, as describedabove, involves comparing mean blood pressures. Other methods ofadjustment may include comparisons of diastolic pressures, systolicpressures, pressures at the end of balloon inflation, andballoon-augmented pressures. The IABP 12 may also monitor the signalfrom catheter pressure sensor 22 for the presence of electrosurgicalinterference, mechanical damage, or any other possible cause of signalerror. If significant error is detected, the IABP 12 would automaticallyrevert to use of the signal from saline pressure sensor 40. Similarly,the IABP 12 may monitor the signal from the saline pressure sensor 40for errors and compensate for these errors by using the signal from thecatheter pressure sensor 22. The IABP 12 may optionally allow a user tomanually select the use of the saline pressure sensor 40 or the catheterpressure sensor 22. Use of the saline pressure sensor 40 may bedesirable in the event that electrosurgical interference wasanticipated.

In an alternate embodiment of the invention, rather than adjustingcatheter pressure sensor 22 signal for drift, saline pressure sensor 40signal may be used solely for numerical display purposes and catheterpressure sensor 22 signal used solely for timing the inflation anddeflation of balloon membrane 30.

Catheter pressure sensor 22 may include any type of sensor capable offitting on the catheter and of measuring blood pressure and producing asignal with a frequency response above approximately 15 Hz. Such sensorsinclude but are not limited to micromanometers such as those produced bycompanies such as Millar, Endosonics, and Radi. These sensors typicallyinclude a small transducer exposed to arterial pressure on one side andoften a reference pressure on the opposite side. Blood pressure deformsthe transducer resulting in a change in resistance which is translatedinto a pressure reading. Alternatively, a fiber optic sensor may be usedin which case pressure sensing line 24 would comprise a fiber opticline. Co-pending application, entitled Intra-Aortic Balloon CatheterHaving a Fiberoptic Sensor, filed on Dec. 11, 2000, herein incorporatedby reference in its entirety, discloses specific embodiments of anintra-aortic balloon catheter having an incorporated fiberoptic sensor.

The present invention, namely the dual use of both a fluid columnpressure sensor and a secondary sensor to measure arterial pressure, isnot limited for use with any specific type of catheter. Furthermore, useof different types of intra-aortic balloon catheters is anticipated.FIG. 3 illustrates a longitudinal cross section of a distal portion of atypical dual lumen intra-aortic balloon (“IAB”) catheter 10 comprisingan outer tube 56, an inner tube 58, a tip 20, and a balloon membrane 30connected on one end to the outer tube 56 and on the opposite end to thetip 20. Tip 20 defines a tip lumen 21. The inner tube 58 is disposedwithin the outer tube 56 and is connected to the tip 20 at its distalend. The inner tube 58 defines an inner lumen 60 and the outer tube 56defines an outer lumen 28. Inner lumen 60 communicates with saline tube38 and is filled with saline or another suitable fluid for pressuresensing (see FIG. 1). Outer lumen 28 is used for shuttling helium oranother appropriate working gas or fluid for inflation and deflation ofthe balloon membrane 30. The outer tube 56 may be coil or braidreinforced and made from polyurethane or polyimide. Inner tube 58 may bemade from polyimide or an alloy with shape memory and superelasticproperties commonly referred to as Ni—Ti, NITINOL™, and other industrynames. Inner tube 58 may be connected to an inner surface of the outertube 56 at one or more points or along the entire length of outer tube56 to enhance pushability, stability, pumping speed, and pressurefidelity. Catheter pressure sensor 22 is embedded in or attached to tip20.

Pressure sensing line 24 connects catheter pressure sensor 22 to IABP 12and is sandwiched between the outer surface of inner tube 58 and asecondary layer 64. Alternatively, the pressure sensing line 24 isembedded in inner tube 58 or attached to the outer surface of inner tube58 (see discussion of FIGS. 3A–3C below). Pressure sensing line 24 willvary dependent on the type of sensor used. If an electricalmicromanometer of half-bridge design is used pressure sensing line 24may consist of three fine wires 62 (see FIGS. 3A–3C), each approximately0.001 inches in diameter. Note that the catheter pressure sensor 22 maybe positioned in alternate locations along IAB catheter 10 as well as ona distal tip of an independent catheter that can be disposed within theinner lumen 58. Dotted box, labeled A, designates another area where thecatheter pressure sensor 22 may be located. In this location catheterpressure sensor 22 is exposed to arterial pressure via tip lumen 21 andis less likely to be damaged upon insertion and placement of IABcatheter 10.

FIGS. 3A–3C illustrate transverse cross sections of inner tube 58 withpressure sensing line 24 connected to inner tube 58 in variousconfigurations. In FIG. 3A, pressure sensing line 24, comprising threefine wires 62, is connected to an outer surface of inner tube 58. InFIG. 3B, pressure sensing line 24 is disposed between inner tube 58 anda thin walled tube 64, which preferably is heat shrinkable. In FIG. 3C,pressure sensing line 24 is embedded in the wall of inner tube 58. Notethat although pressure sensing line 24 is shown running along alongitudinal axis of inner tube 58 it may also be wound helically.

FIG. 4 illustrates a distal portion of another embodiment of the IABcatheter 10, comprising a balloon membrane 30, a tip 20, a co-lumen tube56, an inner lumen extension tube 6, and a catheter pressure sensor 22.Detailed structure of a co-lumen IAB is disclosed in U.S. Pat. No.6,024,693 and U.S. patent application Ser. No. 09/412,718, filed on Oct.5, 1999, both herein incorporated by reference. Tip 20 is connected to adistal end of the balloon membrane 30 and to a distal end of the innerlumen extension tube 66. Tip 20 defines a tip lumen 21. A distal end ofthe co-lumen tube 56 is connected to a proximal end of the balloonmembrane 30 and to a proximal end of the inner lumen extension tube 66.The co-lumen tube 56 may be coil or braid reinforced and made frompolyurethane or poly imide. The preferred material for inner lumenextension tube 66 is an alloy with shape memory and superelasticproperties commonly referred to as Ni—Ti, NITINOL™, and other industrynames. Inner lumen extension tube 66 may also be made from polyimide.The catheter pressure sensor 22 is attached to tip 20 and pressuresensing line 24 which communicates signals generated by the catheterpressure sensor 22 to the IABP 12 (see FIG. 1).

Pressure sensing line 24, as illustrated in FIG. 4, is sandwichedbetween inner lumen extension tube 66 and thin walled tube 64; however,pressure sensing line 24 may be connected to the inner lumen extensiontube 66 in any of the ways illustrated in FIGS. 3A–3C. It is preferredthat pressure sensing line 24 float freely in outer lumen 28, asillustrated in FIG. 4, however, pressure sensing line 24 may beconnected to co-lumen tube 56 in any of the ways illustrated in FIGS.3A–3C. FIG. 4A illustrates a transverse cross section of outer tube 56,taken along line 4A—4A illustrated in FIG. 4, with pressure sensing line24 embedded in the wall. Note that pressure sensing line 24 may beembedded at a different location in co-lumen tube 56 or connected to asurface of co-lumen tube 56.

Co-lumen tube 56 defines two distinct lumens, inner lumen 60 and outerlumen 28. Inner lumen 60 communicates with saline tube 38 (see FIG. 1).Outer lumen 28 communicates with inflate/deflate tube 26 and is used forshuttling helium or another appropriate fluid or gas for inflation anddeflation of balloon membrane 30. Note that the catheter pressure sensor22 may be positioned in alternate locations along IAB catheter 10 aswell as on a distal tip of an independent catheter that can be disposedwithin the inner lumen 58. Dotted box, labeled A, designates anotherarea where the catheter pressure sensor 22 may be located. In thislocation catheter pressure sensor 22 is exposed to arterial pressure viatip lumen 21 and is less likely to be damaged upon insertion andplacement of IAB catheter 10.

FIGS 5A–5C illustrate in detail alternate connections between catheterpressure sensor 22 and a distal end of pressure sensing line 24. In FIG5A a distal end of pressure sensing line 24, extending beyond a distalend of either inner tube 58 (FIG. 3) or inner lumen extension tube 66(FIG. 4), is stripped of insulation 72 exposing wires 62. Catheterpressure sensor 22 comprises a transducer 74 connected to a support 68.Exposed wires 62 are positioned over contacts 70 on support 68 and maybe soldered to support 68. Note that pressure sensing line 24 isconnected to inner tube 58 as shown in FIG. 3B, however, connectionsshown in FIGS. 3A and 3C may also be used.

FIG. 5B illustrates an alternate connection between catheter pressuresensor 22 and pressure sensing line 24, which is embedded in inner tube58. This connection may be used when catheter pressure sensor 22 islocated in alternate location A (see FIGS. 3 and 4). Catheter pressuresensor 22 is identical to the embodiment in FIG. 5A except contacts 70are on the underside of the support 68. Wires 62 are exposed by peelingoff insulation 72 and a portion of inner tube 58 directly above pressuresensing line 24. Catheter pressure sensor 22 fits directly on top ofpressure sensing line 24 such that wires 62 fit over contacts 70. Ratherthan stripping away an entire section of inner tube 58, as in FIG 5B,small holes 78 could be made over the ends of each wire 62, asillustrated in FIG 5C. Solder pads 76 project from an under side ofcatheter pressure sensor 22. Holes 78 can be aligned perpendicular tothe longitudinal axis of the tube or if the wires are wound helically,see dotted lines in FIG 5C, the holes can be aligned along thelongitudinal axis of the inner tube 58. Note that catheter pressuresensor 22 may shifted proximally such that it does not overhang thedistal end of inner tube 58. In such case, an additional hole throughinner tube 58 may be used to allow transducer 74, which is placed oversuch hole, to communicate with inner lumen 60.

Alternatively, transducer 74 may face toward an outer surface ofcatheter tip 20 and sense pressure on the outside of tip 20. This can beaccomplished by using a thicker support 68 or by creating a pocket 90over transducer 74, as illustrated in FIG 6. FIG 6 is a longitudinalcross section of tip 20 and a distal end of inner tube 58 and balloonmembrane 30. Tip 20 has a pocket 90 directly over transducer 74. Pocket90 may contain a gel, fluid, gas, elastomer, or any other flexiblesubstance which both communicates pressure and protects transducer 74.Membrane 92 prevents leakage of gel or other substance from pocket 90.As an alternative to the use of membrane 92, balloon membrane 30 can beextended to cover pocket 90. This catheter pressure sensor 22arrangement can be used for both the dual lumen (FIG 3) and co-lumencatheters (FIG 4).

Note that for both the typical dual lumen and co-lumen catheterarrangements the portion of the inner tube 5.8 disposed within theballoon membrane 30 may be made from a different material from the restof the inner tube 58. This can be accomplished by connecting twoseparate pieces of tubing as disclosed in U.S. Pat. No. 6,024,693,assigned to Datascope Investment Corp., herein incorporated by referencein its entirety.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. A balloon catheter system, comprising: a balloon catheter including aballoon membrane, a tip, a proximal fitting and an outer tube, a distalend of the balloon membrane being connected to the tip, and a proximalend of the outer tube being connected to the proximal fitting; afluid-filled pressure measurement system including a fluid sourceconnected to the proximal fitting via a fluid source line, and apressure sensor for measuring pressure in the fluid source line; and acatheter pressure sensor connected to the balloon catheter.
 2. Theballoon catheter system as claimed in claim 1, wherein the catheterpressure sensor comprises a transducer.
 3. A balloon catheter system,comprising: a balloon membrane; a conduit connected to a proximal end ofthe balloon membrane; a tip connected to a distal end of the balloonmembrane, the tip having a pocket therein; a pressure sensor mounted tothe tip within the pocket; and a protective material overlying thepressure sensor, the protective material being selected from the groupconsisting of a gel, a fluid and a gas.
 4. The balloon catheter systemas claimed in claim 3, wherein the pocket is exposed to an exterior ofthe tip.
 5. The balloon catheter system as claimed in claim 3, whereinthe pressure sensor includes a fiber optic sensor.
 6. The ballooncatheter system as claimed in claim 3, further comprising a membraneoverlying the pocket in the tip.
 7. The balloon catheter system asclaimed in claim 6, wherein the membrane is the balloon membrane.
 8. Aballoon catheter system, comprising: a balloon catheter including aballoon membrane, a tip, a proximal fitting and an outer tube, a distalend of the balloon membrane being connected to the tip, and a proximalend of the outer tube being connected to the proximal fitting; ameasurement system adapted to be fluid-filled, the measurement systembeing connectable to a fluid source and the proximal fitting via a fluidsource line, and being connectable to a first pressure sensor formeasuring pressure in the fluid source line; and a second pressuresensor connected to the balloon catheter, the second pressure sensorincluding a fiber optic sensor.
 9. The balloon catheter system asclaimed in claim 8, wherein the second pressure sensor is adapted tomeasure the pressure of fluid within a blood vessel.
 10. The ballooncatheter system as claimed in claim 8, wherein the second pressuresensor is connected to the tip.
 11. The balloon catheter system asclaimed in claim 8, wherein the tip comprises a tip lumen, an outersurface, and a pocket in the outer surface, and wherein the secondpressure sensor is mounted to the tip with at least one surface of thesecond pressure sensor exposed in the pocket.
 12. The balloon cathetersystem as claimed in claim 11, wherein the pocket is filled with aprotective material.
 13. The balloon catheter system as claimed in claim12, wherein the protective material is a flexible substance.
 14. Theballoon catheter system as claimed in claim 13, wherein the flexiblesubstance is selected from the group consisting of gels, fluids, gasesand elastomers.